The present invention is directed to the electroplating of copper onto a semiconductor structure and, more particularly, to the direct electroplating of copper onto a non-copper plateable layer without an intervening copper seed layer.
In damascene processing, the interconnect structure or wiring pattern is formed within a dielectric layer. Using known techniques a photoresist material is used to define the wiring pattern. The patterned photoresist acts as a mask through which a pattern of the dielectric material is removed by a subtractive etch process such as plasma etching or reactive ion etching. The etched openings are used to define wiring patterns in the dielectric layer. The wiring patterns are then filled with a metal using a filling technique such as electroplating, electroless plating, chemical vapor deposition, physical vapor deposition or a combination thereof. Excess metal can then be removed by chemical mechanical polishing through a process known as planarization.
In a single damascene process, via openings are provided in the dielectric layer and filled with a conducting metal, which is often referred to as metallization, to provide electrical contact between layers of wiring levels. In a dual damascene process, the via openings and the wiring pattern are both provided in the dielectric layer before filling with the conducting metal. Damascene processing followed by metallization is continued for each layer until the integrated circuit device is completed.
Barrier layer films are needed between the dielectric material and the conductive material in order to prevent atoms of the conductive material from migrating into and at times through the dielectric material and into other active circuit device structures. For example, barrier layers are used in conjunction with conductive materials, such as those used in interconnect wiring layers, to isolate the conductive materials from the dielectric material. Migration of conductive material in the device can cause inter-level or intra-level shorts through the dielectric material. In some cases, device functionality can be destroyed.
Migration is a particular concern when copper is used as the conductive interconnect material because copper exhibits relatively high mobility in dielectric materials used in semiconductor structures. Yet, in spite of this problem, copper is a favored material for interconnects because of its superior conductivity and good electromigration resistance. As a result, if copper is used in an interconnect structure, the copper needs to be confined with a barrier layer such as that disclosed in U.S. Pat. No. 6,709,562, the disclosure of which is incorporated by reference herein.
A barrier layer conventionally used in conjunction with copper interconnect structures is tantalum and tantalum nitride. However, because these barrier materials are more reactive than copper, the formation of interfacial oxides can result in poor adhesion properties between the deposited copper and the barrier material. Due to the presence of the contaminating oxides, these conventional barrier materials usually require the deposition of a copper seed layer prior to standard copper electrodeposition in a copper acid bath. Electrodeposition of copper is generally only suitable for applying copper to an electrically conductive layer. As such, the copper seed layer provides the additional purpose of being electrically conductive to facilitate the electrodeposition of copper.
The copper seed layer is typically deposited by a nonconformal vapor deposition process which heretofore has worked well. However, as critical dimensions get smaller, for example less than about 45 nm, the seed layer may pinch off the damascene openings, thereby leading to voids, or may not completely cover the walls of the damascene openings.
Accordingly, a new wiring scheme is being proposed in which ruthenium, platinum, palladium, rhodium and iridium are utilized in conjunction with a barrier layer such as tantalum nitride as a liner in place of the typical metal stack of tantalum nitride and tantalum which requires a copper seed layer.
Others have proposed the use of ruthenium (and like metals such as platinum, palladium, rhodium and iridium) in semiconductor structures. Lane et al. U.S. Pat. No. 6,787,912, the disclosure of which is incorporated by reference herein, discloses a dual barrier structure in which a first layer, for example tantalum nitride or tungsten nitride, is in contact with the dielectric layer while a second layer, for example, ruthenium, rhodium or palladium is in contact with the copper layer. The second layer is touted as being directly electroplateable by copper without the need of a copper seed layer.
However, while ruthenium (and like metals such as platinum, palladium, rhodium and iridium) per se is directly electroplateable by copper, the quality of the copper can suffer if the ruthenium (and like metals such as platinum, palladium, rhodium and iridium) is improperly deposited or if it has not been pretreated to remove deleterious oxides.
Accordingly, it is a purpose of the present invention to have a process for the electrodeposition of copper directly on a ruthenium, platinum, palladium, rhodium or iridium layer (hereafter “plateable layer”).
It is another purpose of the present invention to have a process for the electrodeposition of copper directly on the plateable layer in which the electrodeposited copper is of good quality and tightly adhered to the metallic layer.
It is yet another purpose of the present invention to have a process for the electrodeposition of copper directly on the plateable layer in which a copper seed layer is not required.
These and other purposes of the invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.